Chemistry of hydrocarbon compounds – Aromatic compound synthesis – By isomerization
Reexamination Certificate
2000-06-22
2003-10-21
Dunn, Tom (Department: 1725)
Chemistry of hydrocarbon compounds
Aromatic compound synthesis
By isomerization
C585S482000, C502S060000, C502S064000, C502S066000, C502S085000, C502S074000
Reexamination Certificate
active
06635791
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for pretreating a hydrocarbon conversion catalyst based on an EUO zeolite. The present invention also relates to the activated catalyst obtained and to its use in particular in the field of processes for isomerising aromatic compounds containing 8 carbon atoms.
PRIOR ART
The catalyst activated using the process of the invention can be used for isomerising aromatic compounds containing 8 carbon atoms. In known processes for isomerising aromatic compounds containing eight carbon atoms, a feed which is generally low in para-xylene with respect to the thermodynamic equilibrium of the mixture (i.e., in which the amount of para-xylene is substantially lower than that of the mixture at thermodynamic equilibrium at the temperature under consideration, this mixture comprising at least one compound selected from the group formed by meta-xylene, ortho-xylene, para-xylene and ethylbenzene), and generally rich in ethylbenzene with respect to this same mixture at thermodynamic equilibrium, is introduced into a reactor containing at least one catalyst, under suitable pressure and temperature conditions to obtain from the reactor outlet a composition of C8 aromatic compounds which is as close as possible to the composition of said mixture at thermodynamic equilibrium at the temperature of the reactor.
The para-xylene and optionally meta-xylene or ortho-xylene, which are the desired isomers as they are of great importance in particular for the synthetic fibre industry, are then separated from this mixture.
However, there are a number of problems associated with isomerising C8 aromatic compounds, caused by secondary reactions. Thus in addition to the principal isomerisation reaction, hydrogenation reactions are observed, such as hydrogenation of aromatic compounds to naphthenes, and naphthene ring opening reactions which lead to the formation of paraffins containing at most the same number of carbon atoms per molecule as the naphthenes from which they are formed. Cracking reactions are also observed, such as paraffin cracking which leads to the formation of light paraffins, typically containing three to five carbon atoms per molecule, also dismutation and transalkylation reactions which lead to the production of benzene, toluene, aromatic compounds containing nine carbon atoms and heavier aromatic compounds. All together, those secondary reactions are highly deleterious to the yields of the desired products and depend on the catalyst used for the C8 aromatic compound isomerisation reaction.
The skilled person is well aware that in certain catalytic processes, activation and/or selectivisation procedures have to be carried out on the catalyst to optimise the catalyst performance.
As an example, in the case of a catalyst containing a metal from group VIII of the periodic table, pretreating the catalyst with hydrogen sulphide (H
2
S) is well known. The sulphur contained in the hydrogen sulphide molecule fixes itself to the metal and endows it with improved catalytic properties.
The Applicant's French patent application FR 98.04651 describes a process for activating a C8 aromatic compound isomerisation catalyst by sulphurisation and passivation with ammonia. International patent application WO-A-92/13046 describes an activation process comprising passivating a hydrocarbon catalyst based on a Y zeolite with ammonia. U.S. Pat. No. 5,321,184 describes a process for activating a C8 aromatic compound isomerisation catalyst based on pentasil zeolite by pretreatment under particular conditions.
SUMMARY OF THE INVENTION
The present invention provides a process for pretreating a catalyst used in hydrocarbon conversion processes, comprising the following steps:
a) pretreating a catalyst containing at least one zeolite with structure type EUO and at least one hydrodehydrogenating metal in the presence of a hydrocarbon feed, at a temperature such that a catalyst comprising carbon is obtained;
b) then treating the hydrocarbon feed and the catalyst at a temperature which is lower than the temperature applied in step a).
The present invention also concerns the activated catalyst obtained and the use of the activated catalyst in a process for isomerising a feed comprising xylenes and ethylbenzene.
IMPORTANCE OF THE INVENTION
The pretreatment of the invention can activate the catalyst by coating the active sites with a layer of carbon. In accordance with the invention, the catalyst comprises at least one zeolite with structure type EUO and at least one hydrodehydrogenating metal from the periodic table, and the layer of carbon deposited can attenuate the activity of the metallic and acidic sites, so that when using said catalyst in isomerising aromatic C8 compounds, the loss of aromatic C8 compounds by secondary side reactions of dismutation, transalkylation, hydrogenation and cracking can be reduced, while the selectivity is improved and good ethylbenzene conversion is retained. Further, the use of the process of the invention also comprising sulphurisation and optionally also comprising passivation with ammonia enables the catalyst to be used at lower temperatures and at higher HSVs (weight of feed/weight of catalyst/hour).
DESCRIPTION
The present invention concerns a process for pretreating a catalyst for converting hydrocarbon feeds comprising at least one EUO zeolite and at least one hydrodehydrogenating metal from the periodic table by applying severe temperature conditions when starting off the hydrocarbon conversion process, for a duration sufficient to deposit a certain quantity of carbon on the catalyst, preferably at least 0.1% by weight of carbon with respect to the total catalyst weight, and more preferably at least 0.3%. Following this treatment, the catalyst continues to be brought into contact with the hydrocarbon feed to be converted but under less severe temperature conditions than those applied during the pretreatment.
Further, in a particular implementation of the invention, the pretreatment step can comprise using a particular pressure. Thus, preferably, the pressure applied in step a) is higher than the pressure applied in step b) for the same hydrogen/hydrocarbon ratio.
In this particular implementation, step a) is then characterized in that at least one parameter selected from temperature and pressure is at a value such that the P, T set adopted leads to more favourable conditions for the formation of carbon compared with the conditions used in step b) during which the hydrocarbon conversion reaction proper is carried out.
Pretreatment step a) is carried out for a period of 5 to 120 hours, preferably 20 to 96 hours, the second step b) of the reaction proper being initiated after this first step.
Thus, for example, step a) can be applied at a temperature which is at least 20° C. higher than the temperature of step b), preferably at least 30° C. higher.
Further, the pressure can be varied. Thus, for example, step a) can be carried out at a pressure which is equal to or higher than the pressure of step b), preferably at least 0.3 MPa higher than the pressure in step b), under identical H
2
/HC ratio conditions.
In one implementation of the invention, the catalyst is sulphurised. The catalyst is sulphurised using a sulphur compound, for example hydrogen sulphide or a hydrogen sulphide precursor. The catalyst is sulphurised before the pretreatment of the invention, without the feed and can, for example, be carried out before introducing said catalyst into the reactor, the catalyst then being termed a “pre-sulphurised catalyst”. It can also be carried out using a catalyst which is already in place in the reactor.
In general, before sulphurisation, the compound of the hydrodehydrogenating metal contained in the catalyst is reduced. This pre-sulphurisation step can be carried out with pure hydrogen sulphide or with a precursor, preferably an organic precursor, of hydrogen sulphide which is then decomposed in the reactor.
Non limiting examples of sulphur-containing organic compounds which can be used in the sulphurisation step of
Alario Fabio
Joly Jean-François
Magne-Drisch Julia
Merlen Elisabeth
Institut Francais de Petrole
Millen White Zelano & Branigan P.C.
LandOfFree
Process for pretreating a catalyst based on an EUO zeolite... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for pretreating a catalyst based on an EUO zeolite..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for pretreating a catalyst based on an EUO zeolite... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3164130